1. Field of the Invention
The present invention relates to a die for extruding ceramic honeycomb structural bodies having a plurality of through holes defined by partition walls.
2. Description of Related Art
Generally, as a catalyst carrier and a particulate purifying filter, both used for purifying an exhaust gas from internal combustion engines, or, as a filter used for purifying/deoxidizing a combustion gas of oil or various gases, ceramic honeycomb structural bodies are used. Especially, as a ceramic honeycomb structural body used for the catalyst carrier for purifying an exhaust gas from the internal combustion engines, in order to achieve an improvement of exhaust gas purifying efficiency, a decrease of pressure loss, and a use under high temperatures, it is required to have more thinner partition walls and more larger number of through holes.
To meet the requirements mentioned above, when the ceramic honeycomb structural bodies having more thinner partition wall is to be formed by an extrusion forming method using a die, it is necessary to decrease sizes of slit widths of ceramic batch discharge slits and sizes of hole diameters of ceramic batch supply holes in response to a thinner wall to be required. In this case, there is a drawback such that a die manufacturing becomes extremely difficult and thus larger manufacturing steps are required. Moreover, there are drawbacks on working precision, cost, and time of delivery.
In order to eliminate the drawbacks mentioned above, the applicant proposed a die for extruding ceramic honeycomb structural bodies in U.S. Pat. No. 4,687,433 (Japanese Patent Publication No. 64-7843:JP-B-64-7843). FIG. 5 is a schematic view showing one embodiment of the die for extruding ceramic honeycomb structural bodies disclosed in U.S. Pat. No. 4,687,433. In FIG. 5, a known die 51 for extruding ceramic honeycomb structural bodies comprises a plurality of ceramic batch discharge slits 54 and a plurality of ceramic batch supply holes 52. In the die 51, a plurality of pipes 53 are fitted into at least some of the ceramic batch supply holes 52.
In the die 51 having the construction mentioned above, there is a merit such that an extrusion die for extruding ceramic honeycomb structural bodies having thin walls can be manufactured easily without using a special working means. However, in the die 51 having the construction mentioned above, as shown in FIG. 5, a tip portion 53a of the pipe 53 is inserted into the ceramic batch supply hole 52 to its bottom portion 52a.
Therefore, there is the tip portion 53a of the pipe 53 all around a portion d of the ceramic batch discharge slit 54 in its tip portion 54a. As a result, a ceramic batch to be extruded, which is supplied via the ceramic supply hole 52, is supplied into the ceramic batch discharge slit 54 only through a portion e in the tip portion 54a of the ceramic batch discharge slit 54. In this case, if the ceramic batch discharge slit 54 is arranged by deeply cutting, there is a drawback that only a part of the deep ceramic batch discharge slit 54 is used for a ceramic batch discharge. Moreover, if only a part of the ceramic batch discharge slit 54 is used for a ceramic discharge, it is difficult to discharge uniformly a ceramic batch from the ceramic batch discharge slit 54. In this case, a thickness of the wall after extruding is not uniform, the ceramic honeycomb structural body after extruding is deformed, and, in an extreme case, the ceramic honeycomb structural body can not be extruded.